The present invention is directed to the discovery that the majority of the water contained in municipal waste-water sludge treated by the municipal treatment plants is contained within and between molecular cells. The water molecules contained within the cell, for purposes of this application, shall be referred to as xe2x80x9cintra-cellularxe2x80x9d, water molecules, while the water molecules between the cells and bound thereat via both mechanical and electrical bonding shall be referred to as xe2x80x9cintercellularxe2x80x9d water molecules. It has been the discovery that this intra-cellular and intercellular water makes up the majority of the water in municipal waste-water sludge treated at a municipal treatment plant, which intra-cellular and intercellular water is not typically released by conventional, municipal dewatering methods which process the municipal sludge.
The present invention, also, relates to a system, apparatus and method directed to the safe and effective treatment of biologically-active, municipal waste-water sludges, and more, particularly, to a pulsed, electric-field apparatus and related method for the disinfecting of municipal waste-water sludges in an efficient and effective manner at the level of the individual, molecular cells of the waste material, so as to substantially reduce the resulting volume and weight of the waste material which has to be disposed of by the municipality.
Presently, for all municipal waste-water sewage material, or sludge, treatment of the waste-water sludge by the municipality is done in accordance with applicable rules and regulations. However, there remains a residual bio-solids waste material which contains a significant amount of water that has to be eventually disposed of by the municipality in an environmentally-safe manner. Prior to disposing of this bio-solids waste material, the municipality will attempt to dewater this bio-solids waste material to the maximum extent possible, in order to reduce its disposal cost and any environmental impact. Conventional dewatering techniques that are utilized by the municipal wastewater treatment plants are commonly referred to as (i) a xe2x80x9cbelt filterxe2x80x9d type press, which is a system of multiple rollers and mesh belts through which the bio-solids waste material is caused to travel between, and which cooperate to squeeze some of the water from the bio-solids waste material; or (ii) a dedicated, inline, centrifuge apparatus of some sort, which uses centrifugal force to squeeze some of the water from the bio-solids waste material; or (iii) a plate and frame filter press with hydraulic or mechanical drive, which uses mechanical pressure to dewater discrete batches of the bio-solids waste material. On a typical day in a typical treatment-plant, the bio-solids waste sludge that is treated by the municipality will result in a material mixture containing greater than 90% water-content, and less than 10% solids-content prior to the dewatering process by the municipality. Following the dewatering operation, there is nevertheless a relatively high water content remaining in the resulting, residual, bio-solids waste material, which residual will be concentrated to a mixture containing about 65% to 80% water-content and about 20% to 35% solids-content at the output-end of the municipality""s waste-water treatment apparatus.
An underlying technical problem not addressed nor appreciated by conventional dewatering techniques is that most of the water remains associated with the biologically-active cells which comprise the residual bio-solids waste material; a significant amount of the total water remains inside the cells of this residual bio-solids waste material. That is, water molecules exist on the outside of the cells of the bio-solids waste material, and water molecules also exist on the inside of the cells of the bio-solids waste material. Also, water molecules are bonded between the cells of the bio-solids waste material. Therefore, since the individual cells of the sludge containing the water are not dewatered using conventional dewatering techniques, as the individuals cells have not been irreparably ruptured as a result of the conventional dewatering techniques currently used, so that most of the water in the aggregate within the matrix structure of each cell, it would be highly advantageous if this previously-dewatered, residual bio-solids waste-material sludge could be further dewatered in a continuous and extended manner by substantially removing the water located within the cellular matrix, in a commercially available process. This new approach to the further dewatering and sludge reduction at the cellular level of the residual bio-solids waste material would result in achieving a substantially-reduced volume and mass of the residual waste material requiring disposition by the municipality at the end of its waste-water treatment cycle. Especially when compared to conventional dewatering techniques presently utilized by municipalities, the reduction in the overall volume and weight associated with this residual bio-solids waste material, will result in a significant cost-savings to each municipality as a result of the expected future costs per ton of disposing substantially less residual bio-solids waste material in an environmentally safe manner, as proscribed by applicable rules and regulations.
After many years of study and public hearings, the EPA has recently promulgated EPA 503 regulations that have changed the applicable rules with respect to the disposition of bio-solids waste material by municipalities. The EPA 503 regulations address and promote the safe and effective disposal of bio-solids waste material by municipalities in accordance with the underlying rational and supporting facts of defining two different classes of residual bio-solids waste material, Class xe2x80x9cAllxe2x80x9d and Class xe2x80x9cBxe2x80x9d, and of the need to have an underlying, regulatory process which adopts a different, regulatory approach for each of the two classes of residual bio-solids waste material, and, thereafter, closely regulating the acceptable avenues of disposal for each of the two classes of bio-solids waste material. The difference between Class xe2x80x9cAxe2x80x9d bio-solids waste material and Class xe2x80x9cBxe2x80x9d bio-solids waste materials is directed to the active burden facing the disposal thereof. Class xe2x80x9cAxe2x80x9d bio-solids waste material is a biologically-inert, non-active waste material, and there are no limitations on the disposition of Class xe2x80x9cAxe2x80x9d bio-solids waste material by the municipality. However, Class xe2x80x9cBxe2x80x9d bio-solids waste material is a biologically-active waste material, which may be pathogenic, and, as a result, the disposition of Class xe2x80x9cBxe2x80x9d bio-solids waste material by the municipality is accomplished in a regulatory manner that is consistent with a highly controlled and regulated commodity at appropriate dump sites.
Prior to the recent promulgation of EPA 503 regulations, municipally-treated waste-material, both raw and previously dewatered, biologically active, non-sterile, residual bio-solids waste, could be disposed of by the local municipality by lake, ocean or river dumping; this often resulted in the unfortunate result that the various waters used for disposal would become wild with algae bloom, and the like, indicating severe nutrient enrichment of the water, to the detriment of adjacent land owners and downstream water users. Now, EPA 503 regulations effectively prohibit the disposal of any residual bio-solids waste material by municipalities in this manner. After the promulgation of EPA 503 regulations, there are currently only three approved options that can be used for the disposal of bio-solids waste material, namely: (1) incineration; the burning of bio-solids waste material in accordance with existing rules and regulations; (2) landfilling; there are now specialized landfills (e.g., Class D landfills) that to which the municipality can transport the bio-solids waste material for disposal; and (3) land application; where the bio-solids material is used as a fertilizer and/or soil enhancer. Option (3), land application, is governed by the classification of the residual bio-solids material, Class xe2x80x9cAxe2x80x9d or Class xe2x80x9cBxe2x80x9d. From the viewpoint of the municipality, this dual classification of bio-solids waste material presents the opportunity to utilize new technology to solve the bio-solids waste disposal problem as a result of EPA 503 regulations. Of the above options, (1) and (2) above are the most expensive, with all of the inherent characteristics associated with a very highly regulatory environment. Obviously, it would be a great advantage if a municipality could end up with a process to treat previously dewatered waste material in a manner which will safely and effectively convert, at the cellular level, Class xe2x80x9cBxe2x80x9d bio-solid waste material, which is high regulated with respect to the disposal thereof by the municipality, into a safe Class xe2x80x9cAxe2x80x9d bio-solids waste material, which the municipality can then dispose of in any permissible environmentally safe manner, which allows the municipality to dispose of the solids waste material in a less costly and less regulated manner. Such a novel disinfecting and dewatering process would operate at the cellular level of the bio-solids waste material to rupture the cell wall in a manner non-repairable by the cell structure, thereby facilitating the internal water and related materials within the cell to be squeezed out of the cell structure, so that such is no longer actively contained within the cell structure by the cell. The resulting material is a safe, biologically-inert, solid material.
Furthermore, if such a novel disinfecting and dewatering process could be easily added to existing municipal waste-water sewage treatment plants in a manner which would not require any redesign of the waste-water treatment process or facility, local regulatory approval,and in a manner to facilitate a non-disruptive convenient retrofitable add-on module without any disruption to the municipality""s on-going operations with respect to its existing and regulated waste-water sewage treatment facility at the very end of existing waste-water treatment facilities, such would be a great advantage to the industry.
The various municipal and industrial wastewater treatment plants in the United States generate a large amount of waste activated sludge. The total U.S. market, excluding food and agriculture sectors, is estimated to be about 7xc3x97106 tons/year of waste activated sludge (WAS), on a dry solids (DS) basis(1). About 70 percent of this market is municipal.
This WAS from municipal plants is typically thickened to 2-3 percent solids level and mixed with primary sludge to improve dewatering. The mixed sludge is typically treated with cationic polymers (polyelectrolytes) before being dewatered in belt presses or centrifuges. The typical solids content of the belt pressed mixed sludge is 16-18 percent. If the WAS is dewatered by itself, then the expected solids level is only 10-14 percent.
The pressed/dewatered sludge is mostly disposed off-site at various landfills at a typical fee of $50/ton (wet), which translates to $294/ton (DS), assuming 17 percent solids in the wet sludge. Some sludge is also incinerated or composted; but in both cases, further dewatering/drying is required. The typical cost for incineration is also about $300/ton (DS). Therefore, there is a need to develop alternative technology to reduce the cost of sludge, especially the WAS, disposal.
The present invention is based on the application of a pulsed electric field (PEF) to create holes in or disrupt the bacterial cell membranes in WAS. The effects of PEF on the flocculation/dewatering behavior of WAS has been tested and quantified.
It is known to kill indigenous microorganism, inoculated listeria, yeasts and molds in a pumpable material, such as milk, juice, raw eggs, and the like, by exposing the material to multiple, short pulses of electrical energy in the range of 10-30 KV. range. The electrical field pierces through, and, finally, causes the irreparable rupture of the affected cells of the microorganisms. By breaking down these cells, and preventing their self-repair mechanisms from repairing the cell-membrane damage, the food-product is safer, and the shelf-life of the product is extended. An example of this process in disclosed in U.S. Pat. No. 5,048,404.
In a previous (Phase I) project, it has been demonstrated the laboratory feasibility of pulsed electric field (PEF) for disrupting the biomass in waste activated sludge (WAS) derived from municipal wastewater treatment.
Encouraged by the Phase I results, a pilot plant for testing at one or two wastewater treatment plants that generate WAS has been developed. It has been decided that a pulsed electric field (PEF) system that could handle 0.5 to 1.0 pgm WAS feed be designed. This requires an 8 kw power supply capable of generating 30 kV and pulse generator capable of handling 50 amp peak, current, bi-polar pulses, square wave, 10 xcexcs pulse width, and 3000 pulses/second (pps).
Accordingly, a general object of the present invention is to provide for the further sludge reduction of previously-dewatered, bio-solids, municipal waste-water sludge, using an non-arcing pulsed electric field (PEF) of between 15 KV-100 KV/cm. The application of this voltage to sludge reduction causes massive disruption to the cellular matter as well as the release of bound and intra-cellular liquids.
It is still another object of the present invention to provide a method for cellular rupture via high voltage D.C. pulse at an amplitude of 15,000 to 100,000 volts/CM, or of a variable and sufficient duration, and preferably between 15,000 and 50,000 volts/CM.
It is still another object of the present invention to provide a method for separation of solids and liquids within the bio-solids flow. It is still another object of the present invention to treat animal, paper-pulp, and plant wastes, besides municipal wastes, using electroporation.
In accordance with an illustrative embodiment of the present invention there is provided a pulsed electric-field system for the disinfecting and molecular distruction of biologically-active, waste-water sludge material.
Other objects, features, and advantages of this invention will become apparent from the following detailed description of the preferred embodiment of this invention, as illustrated in the accompanying drawings.